Sometimes, Apple's Mail program says its downloading so many emails, but less than that number actually show up. Like just before I posted this, it said downloading 2 emails, but I only got one (everything goes into the inbox, so emails aren't being filtered into other folders).

I just found the Turn on Logging script in the Mail Scripts folder. So, now it's on, and I'll be able to see what it says the next time this happens.

Meantime, does anyone have any ideas about this? I'm worried that it might be a symptom of someone surreptitiously using my Mac...